Three-dimensional liquid crystal polymer multilayer circuit board including membrane switch and related methods

ABSTRACT

An electronic device includes a multilayer circuit board having a non-planar three-dimensional shape defining a membrane switch recess therein. The multilayer circuit board may include at least one liquid crystal polymer (LCP) layer, and at least one electrically conductive pattern layer thereon defining at least one membrane switch electrode adjacent the membrane switch recess to define a membrane switch. The electronic may further include a compressible dielectric material filling the membrane switch recess. The electronic device may also include at least one spring member within the membrane switch recess.

FIELD OF THE INVENTION

The present invention relates to the field of circuit boards, and, moreparticularly, to circuit boards including a membrane switch providedtherein and related methods.

BACKGROUND OF THE INVENTION

An electronic device may include one or more circuit boards. A typicalcircuit board is a two-dimensional (2D) planar board that mechanicallysupports electronic components. The electronic components may comprise,for example, resistors, capacitors, switches, batteries, and other morecomplex integrated circuit components, i.e. microprocessors. The circuitboard typically comprises a dielectric material, for example, a plasticmaterial.

The circuit board may include conductive traces on the surface forconnecting the electronic components to each other. As electroniccircuitry has become more complex, multilayer circuit boards with atleast two electrically conductive pattern layers have been developed.Typically, the different conductive trace layers of a multilayer circuitboard may be connected through vertically extending vias, which compriseconductive materials, for example, metal. A typical multilayer circuitboard may comprise a plurality of core layers with bonding layerstherebetween affixing the adjacent core layers together. Each core layertypically includes a dielectric layer with electrically conductivepattern layers on the opposing surfaces of the dielectric layer.Typically, during manufacture of the multilayer circuit boards, the coreand bonding layers are stacked together and then heated (laminated) tocause the bonding layer to affix the adjacent core layers together.

Even with the advent of the multilayer circuit board, as the mountedcircuitry has become even more complex, the size of the circuit boardand associated packaging has also increased. This increase in size maypose installation drawbacks in applications where space may be limitedor where fitting a planar two-dimensional circuit board may beproblematic. Three-dimensional (3D) circuit boards are an approach tothis drawback of typical 2D planar circuit boards. As with the typicalplanar multilayer circuit board, the typical 3D circuit board maycomprise a plurality of core layers with bonding layers therebetweenaffixing adjacent layers together.

Advantageously, 3D circuit boards may perform functions beyond thetraditional mechanical support and electrical connection functions ofthe 2D circuit board. In other words, the 3D circuit board may be amultifunctional structure. For example, the 3D circuit board may performmechanical, aerodynamic, and encapsulation functions.

Another approach to growth in circuit board size is integrating externalelectronic components into the circuit board, for example, batteries,and switches. For example, U.S. Pat. No. 7,045,246 to Simburger et al.discloses a thin film battery embedded in a multilayer thin filmflexible circuit board. The circuit board comprises polyimide material,which may have some undesirable material characteristics.

One method to forming 3D circuit boards is disclosed in U.S. patentapplication Ser. No. 11/695,685 to Shacklette et al., also assigned tothe assignee of the present invention, which is incorporated in itsentirety by reference. The method includes thermoforming core layersindividually on a 3D mold structure, stacking the thermoformed corelayers, and laminating the stacked thermoformed layers at even a greatertemperature. One possible drawback of this method is the two-stepheating and cooling process increases manufacturing time and limitsproductivity.

SUMMARY OF THE INVENTION

In view of the foregoing background, it is therefore an object of thepresent invention to provide an electronic device with a multilayercircuit board including a membrane switch therein having effectivesealing and good electrical properties.

This and other objects, features, and advantages in accordance with thepresent invention are provided by an electronic device including amultilayer circuit board having a non-planar three-dimensional shapedefining a membrane switch recess therein. The multilayer circuit boardmay include at least one liquid crystal polymer (LCP) layer, and atleast one electrically conductive pattern layer thereon defining atleast one membrane switch electrode adjacent the membrane switch recessto define a membrane switch. The electronic device may further include acompressible dielectric material filling the membrane switch recess. Theelectronic device may also include at least one spring member within themembrane switch recess. Advantageously, the multilayer circuit board mayprovide a hermetic seal for the membrane switch recess therein.

Additionally, the electronic device may further comprise circuitrycarried by the multilayer circuit board and being coupled to themembrane switch. The at least one LCP layer may further comprise atleast one pair thereof, and the multilayer circuit board may furthercomprise a bonding layer between the at least one pair of LCP layers. Incertain embodiments, the bonding layer may comprise a curable bondinglayer. In other embodiments, the bonding layer may comprise athermoplastic bonding layer.

Another aspect is directed to a method for making an electronic devicecomprising forming a multilayer circuit board having a non-planarthree-dimensional shape defining a membrane switch recess therein. Themultilayer circuit board may comprise at least one liquid crystalpolymer (LCP) layer, and at least one electrically conductive patternlayer thereon defining at least one membrane switch electrode adjacentthe membrane switch recess to define a membrane switch of the electronicdevice. The electrically conductive pattern layer may comprise at leastone of copper, nickel, silver, gold, indium, lead, tin, carbon, andaluminum.

Moreover, the method may further comprise mounting circuitry on themultilayer circuit board, the circuitry being coupled to the membraneswitch. The at least one LCP layer may comprise at least one pairthereof, and the multilayer circuit board may further comprise a bondinglayer between the at least one pair of LCP layers.

Furthermore, the forming of the multilayer circuit board may compriseforming a stacked arrangement comprising at least one pair of LCP layerswith a bonding layer therebetween. The forming of the multilayer circuitboard may also comprise heating and applying pressure to the stackedarrangement to shape the stacked arrangement into a non-planarthree-dimensional shape and concurrently causing the bonding layer tobond together the adjacent LCP layers of the stacked arrangement. Eachof the LCP layers may have a melting temperature, and the bonding layermay have a bonding temperature less than the melting temperature of eachof the LCP layers.

In certain embodiments, the bonding layer may comprise a curable bondinglayer, and the bonding temperature may comprise a curing temperature forthe curable bonding layer. In other embodiments, the bonding layer maycomprise a thermoplastic bonding layer, and the bonding temperature maycomprise a melting temperature for the thermoplastic bonding layer. Theforming of the stacked arrangement may comprise initially forming astacked planar arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method for making a non-planar 3Dmultilayered circuit board according to the present invention.

FIG. 2 is a perspective view of a non-planar 3D multilayer circuit boardmade according to the method of FIG. 1.

FIG. 3 is a schematic cross-sectional diagram of an electronic deviceaccording to the present invention.

FIG. 4 is a flowchart illustrating a method for making the electronicdevice of FIG. 3.

FIGS. 5-12 illustrate an embodiment of the method for making theelectronic device of FIG. 3

FIG. 13 is an isometric view from the top of another electronic deviceaccording to the present invention.

FIG. 14 is a second isometric view from the bottom of the electronicdevice of FIG. 13.

FIG. 15 is a cross-section view of the electronic device of FIG. 13.

FIG. 16 is a flowchart illustrating a method for making the electronicdevice of FIG. 13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

Referring initially to FIGS. 1-2, a flowchart 10 illustrates a methodfor making a non-planar three-dimensional (3D) multilayer circuit board80. From the start (Block 11), the method illustratively includesforming (Block 12) a electrically conductive pattern layer 83 on innersurfaces of liquid crystal polymer (LCP) layers 82, 85, and forming(Block 13) a stacked arrangement, which may be initially planar, thestacked arrangement comprising at least one pair of the LCP layers 82,85 with a bonding layer 84 therebetween.

The electrically conductive pattern layer 83 is illustratively formed oneach LCP layer 82, 85. As will be appreciated by those skilled in theart, the electrically conductive pattern layer 83 may be strippedthereafter. In some embodiments, the electrically conductive patternlayer 83 may be formed on a single LCP layer 82, 85. As will beappreciated by those skilled in the art, the multilayer circuit board 80may be defined by the number of the electrically conductive patternlayers 83 thereon.

The LCP layers 82, 85 may comprise, for example, Rogers F/flex® 3600,3850 core material layers or Nippon Steel Espanex L, Std-Type corematerial layers. Each of the LCP layers may comprise a biaxiallyoriented LCP layer. Advantageously, the biaxially oriented LCP layershave low values for the X and Y coefficients of thermal expansion (CTE)and relatively high values for the Z CTE. For example, Rogers F/flex®3600 and 3850 both have X, Y, and Z values for CTE of 17 (10⁻⁶*1/° C.),17 (10⁻⁶*1/° C.), and 150 (10⁻⁶*1/° C.), respectively.

Advantageously, LCP has electrical properties that may helpful for usein the 3D multilayer circuit 80 board. For example, Rogers F/flex® 3600and 3850 both have a low dielectric constant of 2.9 and a loss tangentat 10 GHz of 0.0025. Moreover, LCP (Rogers F/flex® 3600/3850 and orNippon Steel Espanex L) has hermetic properties and a low water uptakeof 0.04%, and a Young modulus of in the range of 2400-3000 MegaPascals.Advantageously, LCP provides a mechanically robust dielectric material.Moreover, the low loss tangent provides for lower losses in highfrequency circuitry, and the lower dielectric constant provides theability to reduce line spacing and create more compact circuit layouts.

The stacked arrangement illustratively includes the electricallyconductive pattern layer 83, for example, metal traces, on each of theLCP layers 82, 85. The electrically conductive pattern layer 83 maycomprise at least one of copper, nickel, silver, gold, indium, lead,tin, carbon, and aluminum or an alloy thereof. For example, theelectrically conductive pattern layer 83 may comprise a base metal layerof one type and a second metal layer of a second type thereon, in otherwords, a multilayer composite.

The electrically conductive pattern layer 83 may be applied to some orall of the LCP layers 82, 85 before or after the thermoforming andlamination step. As will be appreciated by those skilled in the art,applying the electrically conductive pattern layer 83 to the innersurfaces of the LCP layers 82, 85 may need to be performed before thethermoforming and lamination step.

In certain 3D forms with high aspect ratios, forming the electricallyconductive pattern layers 83 before the thermoforming and laminationstep may be more difficult. In these high aspect ratio 3D circuitboards, the electrically conductive pattern layers 83 may be formedthereafter using, for example, inkjet printing or silk screening. Aswill be appreciated by those skilled in the art, the electricallyconductive pattern layer 83 may comprise any material with suitableconductivity properties. Advantageously, the low value of X-Y CTE andhigh value of X-Y tensile modulus for the LCP layers may prevent breaksand discontinuities in the electrically conductive pattern layer 83during the thermoforming and lamination step. Indeed, the linear (XY)CTE of copper is 17 (10⁻⁶*1/° C.), which advantageously matches the X-YCTE of the LCP layers.

Further advantage stems from the thermoforming step being carried out ata temperature that is significantly below the melting point andapproximately equal to or even as much as 30° C. below the glasstransition temperature of the LCP core layers. Under such conditions,the LCP core layers retain a modulus significantly higher than that ofthe bonding layer 84, a condition that will act to limit and moreuniformly spread the deformation of the LCP layers 82, 85 and the coppertraces thereupon, thereby reducing the chances for a break in the coppertraces 83 caused by excessive elongation.

The method illustratively includes heating and applying pressure to thestacked arrangement to shape the stacked arrangement into a non-planar3D shape and concurrently causing (Block 15) the bonding layer 84 tobond together the adjacent LCP layers 82, 85 of the stacked arrangementto thereby form the non-planar 3D multilayer circuit board. The methodends at (Block 16), an exemplary multilayer circuit board 80 withcircuitry 81 thereon being shown in FIG. 2. In other words, themultilayer circuit board is thermoformed and laminated in one step.

Additionally, the heating (Block 15) may comprise heating in a range of170 to 230° C. Preferably, the heating (Block 15) may comprise heatingin a range of 180 to 220° C. As will be appreciated by those skilled inthe art, the low temperature bound is determined by the respectivetemperature that provides adequate plasticity in the LCP layers 82, 85for thermoforming. In other words, the LCP should be flexible enough tobe shaped or have sufficient plasticity to deform under pressure orvacuum. The high temperature bound is determined by the respectivetemperature that generates excessive plasticity or fluidity in the LCPlayers 82, 85, thereby causing the LCP layers to excessively and/orunevenly deform during thermoforming. The high temperature limit maydepend on the particular choice of LCP material, since the glasstransition temperature and the melting point generally vary with theparticular grade or manufacturer. It is generally preferred to performthe process at the lowest temperature that produces the desiredpermanent shape. A preferred temperature range is from about 180° C. to220° C. The heating (Block 15) may further comprise increasing thetemperature at a constant rate and subsequently decreasing thetemperature at a constant rate, for example, 5° C. per minute and 10° C.per minute, respectively.

Applying pressure (Block 15) may comprise applying pressure using atleast one of a vacuum bag and a press mold, as will be appreciated bythose skilled in the art. The pressure range may be 50-200 pounds persquare inch (psi), for example. Preferably, the pressure range is about80-120 psi. As will be appreciated by those skilled in the art,performing the concurrent thermoforming and lamination step at the lowpressure bound may require a greater process temperature, and performingthe concurrent thermoforming and lamination step at the higher pressurebound may require a lower process temperature.

Moreover, each of the LCP layers 82, 85 has a glass transitiontemperature and a melting temperature above the glass transitiontemperature. Near or above the glass transition temperature, the LCPlayers 82, 85 have a plasticity value for permitting thermoforming. Thebonding layer 84 has a bonding temperature that is significantly belowthe melting point and approximately equal to or even slightly below theglass transition temperature of the LCP layers 82, 85. Advantageously,the steps of bonding/laminating the bonding layer and thermoforming the3D multilayer circuit board 80 may be concurrently performed since theprocess temperature of the bonding layer 84 and the glass transitiontemperature of the LCP layers are within range.

As will be appreciated by those skilled in the art, the layers of the 3Dmultilayer circuit board 80 may be precisely aligned to fit circuitboard features of one layer to the appropriate features in adjacentlayers. For example, the layers may have alignment holes drilled in thembefore/after the thermoforming and lamination step, the holes beingaligned with posts in the press mold to be used in either a mechanicalpress or within a vacuum bag subject to heat and pressure within anautoclave.

In some embodiments, the bonding layer 84 may comprise a curable bondinglayer, and the bonding temperature may comprise a curing temperature forthe curable bonding layer. For example, the bonding layer 84 maycomprise a Bismaleimide-Triazine (BT) resin. For example, in theseembodiments, the bonding layer may comprise Gore Speedboard® C/LFpreimpregnated thermoset bonding layers. The process/curing temperatureof the Gore Speedboard® C/LF preimpregnated thermoset bonding layers isrecommended to be about 180-220° C. As will be appreciated by thoseskilled in the art, other curable bonding layers having a process/curingtemperature within range of the glass transition temperature of LCP maybe used.

In other embodiments, the bonding layer 84 may comprise a thermoplasticbonding layer, and the bonding temperature may comprise a meltingtemperature for the thermoplastic bonding layer. Furthermore, thebonding layer 84 may comprise, for example, a thermoplastic, such as,chlorotrifluoroethylene (CTFE). For example, in these embodiments, thethermoplastic bonding layer may comprise Arlon® 6250 bonding layers. Theprocess/melting temperature of the Arlon® 6250 bonding layers is withinthe range of 120-150° C. As will be appreciated by those skilled in theart, other thermoplastic bonding layers, such as, Arlon® 6700 orRodgers® 3001, having a process/melting temperature within range of theglass transition temperature of LCP may be used.

Referring now to FIG. 3, an exemplary electronic device 20 is nowdescribed. The electronic device 20 illustratively includes a multilayercircuit board 27 having a non-planar three-dimensional shape defining abattery component receiving recess 32 of the electronic device therein.The battery component receiving recess 32 may receive, for example,active materials, electrolytes 22, spacers, an anode, a cathode, andcurrent collectors. The LCP layers 23 may function to provideenvironmental packaging as well as a substrate for circuitry 21 thatalso comprises the electronic device 20.

As will be appreciated by those skilled in the art, the non-planarthree-dimensional shape defining a battery component receiving recess 32therein may be manufactured using the method for making a non-planar 3Dmultilayered circuit board described above. Alternatively, other methodsof thermoforming may be used as will also be appreciated by thoseskilled in the art, for example, the two step lamination andthermoforming process disclosed in U.S. patent application Ser. No.11/695,685 to Shacklette et al.

The multilayer circuit board 27 illustratively includes a plurality ofLCP layers 23, and a plurality of electrically conductive pattern layers26 on some of or all of the LCP layers. The electrically conductivepattern layers 26 define a pair of battery electrodes (contacts) 31, 30adjacent the battery component receiving recess 32. The electricallyconductive pattern layers 26 may comprise at least one of copper andaluminum, for example. More specifically, the battery contacts 31, 30include a cathode contact 30 comprising aluminum and an anode contact 31comprising copper. As will be appreciated by those skilled in the art,other conductive metals may be used.

In some embodiments (not shown), the multilayer circuit board mayinclude a single LCP layer, and a metal foil layer thereon sealing thebattery component receiving recess and the components contained therein.The metal foil layer may comprise, for example, gold, copper, nickel,iron, cobalt, aluminum, molybdenum, silver, zinc, titanium, and alloysthereof. Preferably, the metal foil may comprise copper, aluminum orstainless steel, or one of those metals plated or coated by a secondmetal.

The electronic device 20 may further include anode and cathode activematerials, an insulating spacer, optional metal current collectors, anda battery electrolyte 22 within the battery component receiving recess32. The battery electrolyte 22 may contact the battery electrodecontacts 31, 30 to define a battery, and with the multilayer circuitboard 27 defining exterior portions for the battery. Moreover, thebattery electrolyte 22 may comprise lithium ion electrolyte, forexample.

Advantageously, the electrolyte receiving recess 32 may define theboundaries of the battery components, for example, the electrolyte 22,the anode and cathode active materials, the insulating spacer, the metalcurrent collectors. In other words, the bare battery electrolyte 22 andother battery components may be integrated into the multilayer circuitboard 27 without the typical packaging, for example, foil packaging. Inother embodiments, the battery electrolyte 22 and other batterycomponents may be integrated into the multilayer circuit board 27 withthe typical packaging. The components of the battery, such as, currentcollectors, electrodes, and spacers, may be stacked between the LCPlayers 23 prior to lamination, and the subsequent lamination step mayboth form the LCP around the battery stack and both laminate themultilayer circuit board 27 and seal the battery components in one step.

As will be appreciated by those skilled in the art, the batteryelectrolyte 22 may comprise other electrolyte types. Moreover, theelectrolyte 22 may be inserted into the battery component receivingrecess 32 after thermoforming and lamination of the LCP layers 23, forexample, using an opening 28 (FIGS. 6-12) in the battery componentreceiving recess. Alternatively, the electrolyte packaged cell may beused and inserted before finishing the battery component receivingrecess 32. The battery electrolyte 22 may comprise a solid electrolyteor alternatively liquid electrolyte. In embodiments of the electronicdevice 20 where the non-planar three-dimensional shape defining thebattery component receiving recess 32 is manufactured using the methodfor making a non-planar 3D multilayered circuit board described above, asolid electrolyte may be use and positioned in the LCP layers 23 beforelamination. As will be appreciated by those skilled in the art, thebattery electrolyte 22 may be stable at the thermoforming temperature.Alternatively, if using a liquid electrolyte, the LCP layers 23 may needto be laminated prior to injection through the opening 28 of the liquidelectrolyte due to the high temperature of the thermoforming process andthe likely instability of the liquid electrolyte during thethermoforming process.

Additionally, the electronic device 20 illustratively includes circuitry21 carried by the multilayer circuit board 27 and receiving power fromthe battery, which may be a rechargeable battery or a one-time usebattery. The circuitry 21 may comprise, for example, passive components,display components, or/and active components, such as, an integratedcircuit, etc. The multilayer circuit board 27 illustratively includes abonding layer 25 between the LCP layers 23. In certain embodiments, thebonding layer 25 may comprise a curable bonding layer. In otherembodiments, the bonding layer 25 may comprise a thermoplastic bondinglayer. The electronic device also includes illustratively a perimeterseal 24, which may be the same as or different from the bonding layer25, but may be processed within the same temperature window that allowsthe lamination and the shaping of the electronic device 20.

Referring now also to FIG. 4, a flowchart 33 illustrates a method formaking an electronic device 20. From the start (Block 34), the methodillustratively begins with forming electrically conductive patternlayers 26 on inner surfaces of the LCP layers 23 (Block 36). The methodalso includes forming a stacked arrangement, which may be initiallyplanar, the stacked arrangement comprising at least one pair of LCPlayers 23 with a bonding layer 25 therebetween (Block 37), andpositioning battery components within the LCP layers in alignment withthe inner conductive pattern layers 26 (Block 38). The contacts of theelectronic device 20 may be coated with solder or conductive adhesives,such that the solders may melt or the adhesives may cure during thelamination and thermoforming step.

The method illustratively includes heating and applying pressure to thestacked arrangement to shape the stacked arrangement into a non-planar3D shape and concurrently causing (Block 41) the bonding layer 25 tobond together the adjacent LCP layers 23 of the stacked arrangement tothereby form a battery component receiving recess 32, in other words,forming a multilayer circuit board 27 having a non-planarthree-dimensional shape defining a battery component receiving recesstherein. (Block 41) The multilayer circuit board 27 includes LCP layers23, and a plurality of electrically conductive pattern layers 26 thereondefining a plurality of battery electrodes 30, 31 adjacent the batterycomponent receiving recess 32.

The method also includes positioning (Block 42) a battery electrolyte 22within the battery component receiving recess 32 and contacting thebattery electrodes 30, 31 to define a battery for the electronic device.As will be appreciated by those skilled in the art, the batteryelectrolyte 22 may be inserted into the battery component receivingrecess 32 further upstream, for example, by thermoforming around aprepackaged solid electrolyte cell or by including a solid or gelelectrolyte among the battery components that can withstand thetemperature and pressure of the lamination cycle. The method alsoillustratively includes mounting (Block 43) circuitry 21 on themultilayer circuit board 27 to receive power from the battery, themethod ending at (Block 44).

In another embodiment of the method, a non-planar 3D shape would becreated during the process of (Block 41) using appropriate toolingduring this combined thermoforming and lamination step. The process stepof (Block 41) would then be followed by inserting a pre-packaged batteryor full set of battery components into the battery component receivingrecess 32 (Block 42) and sealing the battery into the non-planar 3Dshape by applying an additional LCP layer 23 held in place by aperimeter seal 24. As will also be appreciated by those skilled in theart, the method described for embedding a battery can be applied toembedding similarly shaped objects, such as, a metal heat spreader or anintegrated circuit.

As will be appreciated by those skilled in the art, an exemplaryimplementation of the method of making the electronic device 20 follows.Referring additionally to FIGS. 5-12, the method is illustrated.Referring specifically to FIG. 6, the vias are formed in the top LCPlayer 23, one via forming the opening 28 for subsequent injection of aliquid electrolyte 22.

In FIG. 7, a slurry coat is applied and the cathode 30 and the anode 31are formed out of aluminum and copper cladding, respectively. A lithiumcobalt oxide electrode 29 is also formed adjacent the cathode 30. Agraphite electrode 90 is also formed respectively adjacent the anode 31.The electrodes are then laminated (FIG. 8) and the battery isstacked-up. Referring specifically to FIG. 9, the top LCP layer 23 isthermoformed to form the battery component receiving recess 32.Referring specifically to FIG. 10, the perimeter seal 24 is laminated onthe cathode 30. In FIG. 11, the electrolyte 22, for example, a liquidfree gel-polymer electrolyte layer, is filled post thermoforming. Theopening is also filled 28 to provide a seal. In FIG. 12, the vias areeither hand painted or plated to tie in battery power.

Referring now to FIGS. 13-15, another exemplary electronic device 45 isillustrated and illustratively includes a multilayer circuit board 53having a non-planar three-dimensional shape. The non-planarthree-dimensional shape defines a membrane switch recess 52 therein. Aswill be appreciated by those skilled in the art, the non-planarthree-dimensional shape defining the membrane switch recess 52 thereinmay be manufactured using the method for making a non-planar 3Dmultilayered circuit board described above. Alternatively, other methodsof thermoforming may be used as will also be appreciated by thoseskilled in the art, for example, the two step lamination andthermoforming process disclosed in U.S. patent application Ser. No.11/695,685 to Shacklette et al.

The multilayer circuit board 53 illustratively includes a pair of LCPlayers 50, 51, and a pair of conductive pattern layers 46, 47 thereondefining a plurality of membrane switch electrodes adjacent the membraneswitch recess 52 to define a membrane switch. Advantageously, althoughtypical membrane switch electrodes are plated in gold or nickel toprevent corrosion, since the thermoformed LCP layers 50, 51 providehermetic or near hermetic properties, the membrane switch electrodes maycomprise bare copper with no plating, thereby reducing manufacturingcost and durability.

The electrically conductive pattern layers 46, 47 may comprise at leastone of copper, nickel, silver, gold, indium, lead, tin, carbon, andaluminum or an alloy thereof. For example, the electrically conductivepattern layers 46, 47 may comprise a base metal layer of one type and asecond metal layer of a second type thereon, in other words, amultilayer composite.

Since it may be helpful to keep the membrane switch recess 52 openduring the thermoforming and lamination step, it may be preferred thatthe lamination be made with a mechanical press that includes a top plateor tooling piece that is machined to produce the desired 3D form of theLCP layer 50. It may be further preferred that the top plate or toolexert a vacuum on the top surface of the LCP layer 50 to ensure that itconforms to the shape of the tooling during the forming and laminationstep.

The electronic device 45 may further include a compressible dielectricmaterial filling the membrane switch recess 52. For example, thedielectric filling material may comprise an air pocket. The electronicdevice 45 may also include at least one spring member 56 within themembrane switch recess 52. Alternatively, certain embodiments may omitthe spring member 56 since the thermoformed LCP layers 50, 51 aremechanically elastic and resilient and may return to preformed 3D shapeafter the membrane switch recess 52 is depressed.

Additionally, the electronic device 45 illustratively includes circuitry54 carried by the multilayer circuit board 53 and being coupled to themembrane switch. Advantageously, the membrane switch may be coupled toand control the circuitry 54 integrated on the multilayer circuit board53. The multilayer circuit board 53 includes a bonding layer 55 betweenthe LCP layers 50, 51.

Referring now additionally to FIG. 16, a flowchart 60 illustrates amethod for making an electronic device 45. From the start (Block 61),the method illustratively begins with forming electrically conductivepattern layers 46, 47 on inner surfaces of LCP layers 50, 51 to defineat least one pair of switch electrodes (Block 62). The method alsoincludes forming a stacked, arrangement, which may be initially planar,the stacked arrangement comprising at least one pair of patterned LCPlayers 50, 51 with a bonding layer 55 therebetween (Block 63). Thestacked arrangement includes at least one electrically conductivepattern layer 46, 47 on each of the LCP layers 50, 51.

The method also includes heating and applying pressure and a selectivevacuum to the stacked arrangement, and shaping (Block 65) the stackedarrangement into a non-planar 3D shape and concurrently causing thebonding layer 55 to bond together the adjacent LCP layers 50, 51 of thestacked arrangement to thereby form the 3D multilayer circuit board 53.In other words, the method includes forming a multilayer circuit board53 having a non-planar three-dimensional shape defining a membraneswitch recess 52 therein.

The method illustratively includes forming (Block 66) electricallyconductive pattern layers 46, 47 on at least one of the outer surfacesof the LCP layers 50, 51 for defining at least one membrane switchelectrode adjacent the membrane switch recess 52 to define a membraneswitch, i.e. to complete the circuit interconnects and optionally toconnect to any surface mount components or circuitry 54. As will beappreciated by those skilled in the art, the electrically conductivepattern layers 46, 47 may be formed further upstream in the method, forexample, during the process at Block 62. Moreover, the methodillustratively includes mounting the circuitry 54 (Block 70) on themultilayer circuit board 53, the circuitry being coupled to the membraneswitch. The method ends at (Block 71).

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

That which is claimed is:
 1. An electronic device comprising: a multilayer circuit board having a non-planar three-dimensional shape defining a sealed membrane switch recess therein; said multilayer circuit board comprising at least one liquid crystal polymer (LCP) layer, and at least one electrically conductive pattern layer defining at least one membrane switch electrode within the sealed membrane switch recess to define a sealed membrane switch; circuitry on said multilayer circuit board and coupled to said at least one electrically conductive pattern layer; a compressible dielectric material filling the sealed membrane switch recess; and at least one spring member within the sealed membrane switch recess.
 2. The electronic device according to claim 1 wherein said at least one LCP layer comprises at least one pair thereof; and wherein said multilayer circuit board further comprises a bonding layer between the at least one pair of LCP layers.
 3. The electronic device according to claim 2 wherein said bonding layer comprises a curable bonding layer.
 4. The electronic device according to claim 2 wherein said bonding layer comprises a thermoplastic bonding layer.
 5. The electronic device according to claim 1 wherein said multilayer circuit board defines exterior portions for the sealed membrane switch.
 6. The electronic device according to claim 1 wherein said at least one electrically conductive pattern layer comprises at least one of copper, nickel, silver, gold, indium, lead, tin, carbon, and aluminum.
 7. An electronic device comprising: a multilayer circuit board having a non-planar three-dimensional shape defining a sealed membrane switch recess therein; said multilayer circuit board comprising at least one pair of liquid crystal polymer (LCP) layers, a bonding layer between the at least one pair of LCP layers, and at least one electrically conductive pattern layer on each of the LCP layers and defining at least one membrane switch electrode within the sealed membrane switch recess to define a sealed membrane switch; circuitry carried by said multilayer circuit board and being coupled to said at least one electrically conductive pattern layer, said multilayer circuit board defining exterior portions for the membrane switch; a compressible dielectric material filling the sealed membrane switch recess; and at least one spring member within the sealed membrane switch recess.
 8. The electronic device according to claim 7 wherein said bonding layer comprises a curable bonding layer.
 9. The electronic device according to claim 7 wherein said bonding layer comprises a thermoplastic bonding layer. 